This invention relates to polysulfide polymers.
Polysulfide polymers are well-known and have been used commercially for many years. See, for example, U.S. Pat. Nos. 1,890,191 and 2,466,963. Such polysulfide polymers are prepared by copolymerizing metal polysulfides and polyfunctional aliphatic hydrocarbons such as ethylenedichloride, 1,2,3-trichloropropane and bis 2-chloroethyl formal. A very high molecular weight rubber is thereby formed, which is then cleaved with sodium hydrogen sulfide and sodium sulfite to yield a lower molecular weight mercaptan-terminated polymer. Although these mercaptan-terminated polymers may be cured by the use of oxidants such as metal oxides to form rubbers with many desirable properties, the mercaptan end groups of these polymers impart a strong, disagreeable odor which limits the practical utility of these polymers.
Grotenhuis et al. disclose in U.S. Pat. No. 2,445,191 that, in order to increase the resistance of polysulfides to cold flow, unsaturated aliphatic compounds may be incorporated into the copolymer such that there is one carbon-carbon double bond for each 100 to 300 carbon atoms. Grotenhuis further notes that a monosubstituted aliphatic compound may be employed to limit the molecular weight of the copolymers. However, the use of such copolymers has not proven commercially practical because said copolymers do not cure well.
Styrene is also known to react with sulfur to produce a high molecular weight polymer, but it rapidly depolymerizes to give 2,4-diphenylthiophene. See Blight et al., Adv. Chem. Ser. 165 13 (1978).
The copolymerization of bis(p-vinylbenzyl)disulfide with styrene and divinylbenzene to form a crosslinked polymer is reported by Wulff and Schulze in Angen Chem. Int. Ed. Engl. Vol. 17, pp. 537-80 (1978). The disulfide linkages are then reduced to mercaptan groups having a predetermined stereochemical relationship. Again, the presence of mercaptan groups imparts an undesirable odor to the crosslinked polymer, greatly limiting its utility.
In view of the deficiencies of previously known polysulfide resins, it is highly desirable to produce a curable polysulfide resin which is substantially free of offensive odors.